1. Field of the Invention
The invention relates to the combination of an organic substrate and glass strands coated with a sizing composition constituted by a solution with a solvent content of less than 5% by weight, the solution comprising a mixture of components which can be polymerized and/or cross-linked by heat treatment, amongst the said components, at least 60% being components with molecular weights (Mw) of less than 750, and from 0 to 25% by weight being coupling agents, lubricating agents, stabilizing agents, polymerization initiators and/or catalysts, the said agents and initiators optionally being capable of being polymerized and/or cross-linked, the said sizing composition being non-polymerized, and of the subsequent subjection of the assembly to heat treatment and/or to the action of actinic radiation.
2. Discussion of the Background
The present invention relates to a method of manufacturing a composite material formed by an organic substrate reinforced by glass strands.
The manufacture of a composite material of this general type has been the subject of very many publications, particularly patent applications or patents.
In general, glass strands are coated, during their manufacture, with a sizing composition, the composition of which depends upon the nature of the organic substrate to be reinforced thereby.
The sizing composition, which is deposited on the glass filaments before the latter are assembled into at least one strand, should possess certain characteristics and should confer various properties on the strand. In particular, the sizing composition should be stable and should retain a constant composition in spite of the shear forces constantly brought about within the sizing composition by the filaments which pass through it at speeds of the order of several tens of meters per second.
The sizing composition should then protect the filaments from abrasion caused by the inevitable friction of the strand on various surfaces. It should also ensure the integrity of the strand, that is, the bonding together of the filaments which make it up. This characteristic is important because it not only enables a strand to be extracted easily from a winding (a very common arrangement for glass strands) but also limits the number of filaments which rub directly against all of the devices for guiding the strand. When the strand is intended to reinforce an organic substrate, the sizing composition should also facilitate the wetting of the filaments which make up the strand, by the said substrate.
The achievements of good integrity and of a good capacity to be wetted by the organic substrate are generally incompatible. In general, the greater the integrity of the strand, the stronger is the bonding between the filaments and the more difficult it is for the organic substrate to penetrate the interior of the strand. This difficulty in impregnating a strand with the organic substrate is even more marked when the strand has been twisted and is used as a reinforcement in the form of a fabric.
Finally, when the glass strand is intended to reinforce organic substrates, the sizing composition deposited on the filaments should be chemically compatible with the substrates.
Almost all known sizing compositions are sizing compositions in an aqueous phase in the form of solutions, or much more often, in the form of suspensions or emulsions, in water.
Before they are combined with an organic substrate, the glass strands thus sized have to be dried to eliminate the water which becomes useless or even a nuisance. In order to do this, the windings are subjected to temperature cycles generally of between 110 and 150.degree. C. for periods which may reach and exceed 16 hours. The quantity of water to be evaporated is large since it represents, on average, at least 10 to 15% by weight of the winding. This operation requires special installations and energy consumption, the cost of which increases production costs.
Moreover, the drying of the winding may sometimes detract from the quality of the strand when it causes uneven migration of the sizing components through the turns of the windings.
In order to mitigate these problems, it is known to dry the strand (U.S. Pat. No. 3,853,605) or the filaments (WO-92/05122) directly, before the formation of the winding.
The drying of the strands during the drawing step necessitates the installation of devices such as ovens beneath each die. Moreover, the effectiveness of this drying method is closely linked with the manufacturing conditions such as the quantity of water on the strand, the composition of the sizing composition, the drawing speed, the number of filaments and their diameter. etc.
In rare cases of sizing compositions composed solely of organic constituents, the glass strands coated with such sizing compositions are often subjected to a special treatment before they are reeled on a rotating support. The purpose of this treatment is to bring about a modification of the sizing composition on the strand before it is reeled, such that the sizing composition does not give rise to excessive bonding of the turns of the winding to one another, which bonding can make the strand difficult if not impossible to unwind. This treatment consists, for example, of heating of the layer of filaments coated with the sizing composition so as to eliminate the solvent from the said sizing composition before the strand is formed by the assembly of the said filaments (U.S. Pat. No. 3,425,862) or polymerization of the sizing composition by the subjection of the strand to the action of ultra-violet radiation (U.S. Pat. No. 5,049,407) over at least a portion of its path. Here again, this type of treatment necessitates the installation of devices beneath each die and does not avoid the search for the best possible compromise between the integrity of the strand and its capacity to be wetted by an organic substrate.
An integral strand coated with a purely organic sizing composition can be produced without having been subjected to heat or other treatment; it is the sizing composition itself which bonds the filaments together. The patent U.S. Pat. No. 4,530,860 describes sizing compositions of this type which comprise a large percentage of film-forming agents, the essential role of which is to confer the integrity necessary for the handling of the strand.
The mechanical characteristics of a composite material formed by an organic substrate reinforced by glass strands depend upon the quality of the adhesion of the strands to the substrate. This adhesion results from the capacity of the strands to be wetted by the substrate which depends, in particular, upon the nature of the sizing composition, upon its distribution on the strand, and upon the condition under which the sizing composition has to bring about the cohesion of the filaments forming the strand. Now, these different variables are closely linked to the aforementioned conditions of manufacture of the strand, which impede the production of a strand with the best possible impregnation by an organic substrate.